As described in the above-referenced patent, U.S. Pat. No. 5,074,381, the contents of which are incorporated by reference herein, oil in components such as turbines is periodically checked to determine any presence of metallic or other solid particulates to determine the cleanliness of the turbine system. During shutdown for repair or maintenance, for example, oil is flushed through a turbine to oil handling equipment, such as piping, and circulated through a strainer assembly for a predetermined period of time. The strainer is then removed and any solid particulates collected by the strainer analyzed.
When performing an oil flush on a turbine-generator, samples are taken at a plurality of locations in the system, with a strainer incorporated into the system at several locations, or sampling points. Such locations include each bearing, the main oil pump circuit, a point in the air side seal oil, a point on the hydrogen side seal oil, the high pressure operating oil, and the control oil. Only turbine-generators with mechanical hydraulic controls require sampling at the latter two sample points. In order to take a sample, oil is diverted through the strainer for about 30 minutes. This, typically, provides for the passage of between about 3000 to 5000 gallons (11,000 to 19,000 liters) of oil to pass through the screen of a sampling device. A particle count is measured on a 150 mesh sampling screen and the measurement compared to an acceptable criterion. This method provides an accurate representation of pipe cleanliness, whereas, a grab sample, out of the oil reservoir, is a more representative test of oil cleanliness.
Current procedures for taking an oil sample use a basket type strainer lined with a 150 mesh stainless steel screen through which the oil is passed. This basket-type strainer was originally designed for use as a filter and not for collection and analyzing of solid particles in the particle size range of 0.005 to 0.010 inch (0.0127 to 0.0254 cm) range. The original design of such a conventional strainer was meant to capture solid particles of a size above 0.125 inch (0.317 cm) in diameter. These strainers are conventionally lined with a 150 mesh screen to collect small diameter particles.
For this reason, the strainer basket is difficult to wash down when taking a particle count. An oil flush of a three cylinder, nine bearing turbine-generator with mechanical hydraulic control system, for example, could require fourteen locations where basket strainers were inserted and approximately forty samples taken and analyzed. This number of samples requires a great deal of time just to clean the baskets to ensure that a "clean" strainer will not foil a particle count.